To Identify the Lead Blocker or Blocking Chain

--for simplified view, use the following script
SET NOCOUNT ON
GO
SELECT SPID, BLOCKED, REPLACE (REPLACE (T.TEXT, CHAR(10), ' '), CHAR (13), ' ' ) AS BATCH
INTO #T
FROM sys.sysprocesses R CROSS APPLY sys.dm_exec_sql_text(R.SQL_HANDLE) T
GO
WITH BLOCKERS (SPID, BLOCKED, LEVEL, BATCH)
AS (
SELECT SPID,
BLOCKED,
CAST (REPLICATE ('0', 4-LEN (CAST (SPID AS VARCHAR))) + CAST (SPID AS VARCHAR) AS VARCHAR (1000)) AS LEVEL,
BATCH FROM #T R
WHERE (BLOCKED = 0 OR BLOCKED = SPID)
AND EXISTS (SELECT * FROM #T R2 WHERE R2.BLOCKED = R.SPID AND R2.BLOCKED <> R2.SPID)
UNION ALL
SELECT R.SPID,
R.BLOCKED,
CAST (BLOCKERS.LEVEL + RIGHT (CAST ((1000 + R.SPID) AS VARCHAR (100)), 4) AS VARCHAR (1000)) AS LEVEL,
R.BATCH FROM #T AS R
INNER JOIN BLOCKERS ON R.BLOCKED = BLOCKERS.SPID WHERE R.BLOCKED > 0 AND R.BLOCKED <> R.SPID
)
SELECT N' ' + REPLICATE (N'| ', LEN (LEVEL)/4 - 1) +
CASE WHEN (LEN(LEVEL)/4 - 1) = 0
THEN 'HEAD - '
ELSE '|------ ' END
+ CAST (SPID AS NVARCHAR (10)) + N' ' + BATCH AS BLOCKING_TREE
FROM BLOCKERS ORDER BY LEVEL ASC
GO
DROP TABLE #T
GO

--for detailed view, use the following script
IF OBJECT_ID('tempdb.#Blocks') IS NOT NULL
 DROP TABLE #Blocks
SELECT spid
 ,blocked
 ,REPLACE (REPLACE (st.TEXT, CHAR(10), ' '), CHAR (13), ' ' ) AS batch
INTO #Blocks
FROM sys.sysprocesses spr
 CROSS APPLY sys.dm_exec_sql_text(spr.SQL_HANDLE) st
GO

WITH BlockingTree (spid, blocking_spid, [level], batch)
AS (
 SELECT blc.spid
 ,blc.blocked
 ,CAST (REPLICATE ('0', 4-LEN (CAST (blc.spid AS VARCHAR))) + CAST (blc.spid AS VARCHAR) AS VARCHAR (1000)) AS [level]
 ,blc.batch
 FROM #Blocks blc
 WHERE (blc.blocked = 0 OR blc.blocked = SPID) AND
 EXISTS (SELECT * FROM #Blocks blc2 WHERE blc2.BLOCKED = blc.SPID AND blc2.BLOCKED <> blc2.SPID)
 UNION ALL
 SELECT blc.spid
 ,blc.blocked
 ,CAST(bt.[level] + RIGHT (CAST ((1000 + blc.SPID) AS VARCHAR (100)), 4) AS VARCHAR (1000)) AS [level]
 ,blc.batch
 FROM #Blocks AS blc
 INNER JOIN BlockingTree bt
 ON blc.blocked = bt.SPID
 WHERE blc.blocked > 0 AND blc.blocked <> blc.SPID
)
SELECT N'' + ISNULL(REPLICATE (N'| ', LEN (LEVEL)/4 - 2),'')
 + CASE WHEN (LEN(LEVEL)/4 - 1) = 0 THEN '' ELSE '|------ ' END
 + CAST (bt.SPID AS NVARCHAR (10)) AS BlockingTree
 ,spr.lastwaittype AS [Type]
 ,spr.loginame AS [Login Name]
 ,DB_NAME(spr.dbid) AS [Source database]
 ,st.text AS [SQL Text]
 ,CASE WHEN cur.sql_handle IS NULL THEN '' ELSE (SELECT [TEXT] FROM sys.dm_exec_sql_text (cur.sql_handle)) END AS [Cursor SQL Text]
 ,DB_NAME(sli.rsc_dbid) AS [Database]
 ,OBJECT_SCHEMA_NAME(sli.rsc_objid,sli.rsc_dbid) AS [Schema]
 ,OBJECT_NAME(sli.rsc_objid, sli.rsc_dbid) AS [Table]
 ,spr.waitresource AS [Wait Resource]
 ,spr.cmd AS [Command]
 ,spr.program_name AS [Application]
 ,spr.hostname AS [HostName]
 ,spr.last_batch AS [Last Batch Time]
FROM BlockingTree bt
 LEFT OUTER JOIN sys.sysprocesses spr
 ON spr.spid = bt.spid
 CROSS APPLY sys.dm_exec_sql_text(spr.SQL_HANDLE) st
 LEFT JOIN sys.dm_exec_cursors(0) cur
 ON cur.session_id = spr.spid AND cur.fetch_status != 0
 JOIN sys.syslockinfo sli
 ON sli.req_spid = spr.spid AND sli.rsc_type = 5 AND
 OBJECT_NAME(sli.rsc_objid, sli.rsc_dbid) IS NOT NULL
ORDER BY LEVEL ASC